FR3113988A1 - DEVICE FOR THE FORMATION OF POLES OF A ROTOR - Google Patents

Abstract

The invention relates to a device intended to form, by an injection process of a magnetic composite mixture, the poles of a rotor. The invention relates in particular to a device allowing the formation of the poles of the rotor without damaging the latter. Figure for abstract: figure 1.

Description

DEVICE FOR THE FORMATION OF POLES OF A ROTOR

The invention relates to the field of magnetism and relates in particular to a device making it possible to manufacture magnetic sections by injection. In particular, the invention relates to a device for forming the poles of a rotor by injecting a magnetic composite mixture into the cavities of a rotor body. The application of a magnetic field during the injection makes it possible to polarize the magnetic composite mixture which, when it cools, freezes, and retains a permanent magnetization.

PRIOR ART

It is now envisaged to implement injection processes for the production of the magnetic poles of a rotor. The latter are, in this respect, formed of one or more magnetized sections housed in cavities of said rotor. As specified in document DE 10 2016 224 249, the methods include in particular a hot injection of a liquid composite mixture, made of plastic material and coercive magnetic powder, into the cavities of the body of the rotor which play the role of mould. During a cooling step, the composite mixture freezes and then adopts the shape imposed on it by the cavities in order to form the magnetic sections.

These injection processes, as envisaged, are not limited to the sole production of parallelepiped magnetized sections, and give access to any type of shape, thus making it possible to confer on the magnetic poles a better magnetic efficiency. The magnetized sections are, moreover, obtained in a single step, without further handling or gluing step.

In addition, the choice of shapes of magnetized sections likely to be obtained, the injection makes it possible to envisage arrangements without vacuum, and of a lower density than that of sintered magnets. These aspects make it possible to improve the general balance of the rotor, and to make the latter less sensitive to the centrifugal forces to which it is subjected when it is rotated. It is thus possible to impose higher rotational speeds on such rotors.

Finally, these magnets, manufactured by injection using the method described in document DE102019107394, are likely to have a higher resistivity of more than two orders of magnitude than that of magnets formed using a sintering process.

Nevertheless, despite these advantages, the injection processes are, as they stand, not satisfactory.

Indeed, the composite mixture, in order to form a magnetized section, must be subjected to a relatively high magnetic field, and in particular of the order of 1 tesla. In this respect, it is generally proposed to implement a magnetic ring, formed of a plurality of magnets (as described in documents JP 2014-192980 and WO2013103118), and at the center of which the rotor is arranged during the injection of the composite mixture. The magnets forming the ring are generally regularly distributed angularly, and each in correspondence with one or more cavities in the or which will be formed a magnetic pole. Thus, the composite mixture injected into a given cavity is subject to the magnetic field, in terms of intensity and orientation, of the magnet with which said cavity is in correspondence. Thus, when it cools to solidify, the composite mixture retains the polarization imposed by the magnet, and forms a magnetized section.

However, in order to be able to impose sufficient magnetization on the composite mixture during its cooling, it is generally required to implement a magnetic ring which has a diameter 2 to 3 times greater than the rotor. In other words, the consideration of a large rotor, and in particular of a diameter greater than 10 cm, requires the implementation of very large masses of magnets.

This last aspect, due to the magnetic interactions between magnets, makes the assembly of said magnets relatively complicated.

Furthermore, the magnetic field of the magnets forming the magnetic ring, which is permanent, is likely to interact with any magnetic part placed in its immediate environment and, due to its intensity, poses obvious safety problems.

Furthermore, the viscosity of the composite mixture makes it necessary to inject it at relatively high pressures, in particular between 500 and 1000 bars, which are liable to damage the rotor, for example by deforming it.

Also in order to overcome, at least partially, the problems relating to the safety and complexity of the assembly of the magnets forming the ring, it may be proposed to replace them with induction coils.

However, the magnetic field likely to be imposed by a coil at the level of the cavity or cavities with which said coil is in correspondence is not uniform within the same cavity and from one cavity to another. This effect directly affects the magnetization of the magnetized sections and adversely affects the performance of the rotor.

An object of the present invention is therefore to propose a device for the formation of magnetic sections of a rotor which makes it possible to limit damage to the rotor during the injection of the composite mixture.

Another object of the present invention is to propose a device for forming magnetic sections of a rotor, which is capable of implementing a system for injecting the composite mixture at high pressure while preserving the integrity of the rotor.

Another object of the present invention is also to propose a device for forming magnetized sections of a rotor, which makes it possible to guarantee a better distribution of the magnetic field imposed at the level of the cavities of the rotor.

The aims are, at least in part, achieved by a device for forming the poles of a rotor, each pole comprising one or more magnetized sections formed in a series of injection cavities, called the pole series, of the rotor, by injection of a composite material in said cavities, the device comprises:
- a rotor, arranged in a cylindrical cavity, said rotor being delimited by an upper face and a lower face which are flat and parallel to each other, and connected by a lateral section of cylindrical shape, the polar series have a regular angular distribution around a axis of revolution of said rotor, and the injection cavities emerge at the level of the lower face and the upper face;
- a means of injecting magnetic composite material, in the liquid state, into the injection cavities at a pressure P lower than a predetermined pressure;
- polarization modules regularly distributed around the axis of revolution of the cylindrical cavity, each polarization module comprising, along a main axis, a magnetic section intended to impose a magnetic polarization field on the composite material capable of being injected into the injection cavities, and a magnetic pole, the magnetic poles comprising a surface, called the lateral holding surface, all of the lateral holding surfaces defining a lateral surface of the cylindrical cavity;
- locking means arranged so as to maintain the lateral support surfaces pressing against the lateral section of the rotor, so that the lateral support surfaces compensate for the stresses imposed on the rotor during the injection of the composite material at the pressure p.

According to one mode of implementation, each polarization module is arranged in correspondence with a different polar series so as to be able to impose the magnetic field on the magnetic composite material capable of being injected into the injection cavities of said polar series.

According to one mode of implementation, said device comprises an upper holding member and a lower holding member held in abutment by second locking means against, respectively, the upper face and the lower face, and so as to compensate for stresses likely to be imposed on the rotor during the injection of the composite material at the pressure P.

According to one mode of implementation, the injection means is arranged to inject magnetic composite material at the level of the upper face of the rotor.

According to one mode of implementation, the injection means cooperates with the upper holding member for the injection of the magnetic composite material into the injection cavities.

According to one mode of implementation, the upper holding member comprises a plurality of distribution channels arranged for the collective injection of the magnetic composite material into each of the injection cavities.

According to one mode of implementation, the injection cavities of a polar series are symmetrical with respect to a plane formed by the axis of revolution and by the main axis of the polarization module in correspondence with the polar series concerned, and are arranged one behind the other along said main axis.

According to one mode of implementation, the device comprises magnetic field distributor means intended to distribute the magnetic field imposed by each polarization module to the injection cavities of the polar series with which said module.

According to one mode of implementation, the distributor means comprise inserts, each insert forming a magnetic bridge between a polarization module and injection cavities of the polar series with which said module is in correspondence.

According to one mode of implementation, the magnetic bridge is formed between the polarization module and the injection cavities of the polar series likely to be screened by other injection cavities of this same polar series.

According to one mode of implementation, the inserts are inserted into cavities of the upper and lower holding members, and advantageously comprise a ferromagnetic material.

According to one mode of implementation, the magnetic section comprises a coil carrier around which is formed a coil which, when passed through by an electric current, generates the magnetic field necessary for the magnetization of the magnetic composite mixture capable of being injected into the injection cavities.

Other characteristics and advantages will appear in the following description of a device for forming poles of a rotor according to the invention, given by way of non-limiting examples, with reference to the appended drawings in which:

is a schematic representation of a device for forming poles of a rotor according to the present invention, the cylindrical cavity being empty;

is a schematic representation of a rotor body implemented within the scope of the present invention;

is a schematic representation in perspective of a polarization module capable of being implemented within the scope of the present invention;

are schematic representations of a lower holding member, respectively, with magnetic inserts positioned in housings of the holding member, and with the same magnetic inserts arranged around said member;

is a representation of an upper holding member with magnetic inserts positioned in housings of the holding member;

is a schematic representation e of a rotor after injection of the magnetic composite mixture, in particular this schematic representation shows an imprint of the network of distribution channels of the injection means;

is a schematic representation of the device 10 according to the present invention;

is a graphic representation of a simulation and a measurement of the magnetic field (along the horizontal axis in mT) as a function of the angular position (horizontal axis in degrees) at the level of the lateral section of a rotor manufactured with the device according to the present invention.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

The present invention relates to a device intended to form, by an injection process of a magnetic composite mixture, the poles of a rotor.

In this respect, FIG. 1 is a schematic representation of the device 10 according to the present invention, said device resting in particular on a flat support 60, also called the mold carcass plate.

The device 10 comprises in particular a cylindrical cavity 20 intended to house the body of a rotor 30 (FIG. 2) during the implementation of the present device 10 for the formation of the poles of said rotor.

Each pole comprises in this respect one or more magnetized sections formed in a series of injection cavities 34a, called pole series 34, of the rotor, by injecting a composite material into said cavities.

The rotor body 30, generally of cylindrical shape, is delimited by an upper face 31 and a lower face which are flat and parallel to each other, as well as a lateral section 33 connecting the upper face 31 and the lower face.

The polar series have a regular angular distribution around an axis of revolution of said rotor, and the injection cavities 34a open out at the level of the lower face 31 and the upper face.

The body of the rotor 30 can advantageously comprise a stack, along the axis of revolution, of magnetic sheets glued together.

For example, the magnetic sheets can comprise at least one of the materials chosen from: steel, stainless steel, FeSi, FeCo.

The device 10 comprises means for injecting magnetic composite material into the injection cavities at a pressure P lower than a predetermined pressure. The magnetic composite material is in particular injected in the liquid state at high temperature, for example at a temperature between 150°C and 320°C. The magnetic composite material is also suitable for congealing (solidifying) and adopting the shape imposed on it by the injection cavity into which it is injected during a cooling phase.

The magnetic composite material may in particular comprise plastic material mixed with a coercive magnetic powder. For example, the plastic material and the coercive powder can represent, respectively, 40% and 60% of the volume of the composite material.

The choice of plastic material and coercive powder may depend on the intended application and the magnetic efficiency of the rotor. By way of example, the plastic material may comprise a polyamide of the PA12 type. Such a polyamide makes it possible to achieve a high charge rate and therefore a better magnetic performance. Alternatively or additionally, the plastic material may comprise poly(phenylene sulphide), PPS, which is a resistant polymer, is capable of being used at a temperature which may reach 150°C, or even 180°C.

The magnetic powder may comprise NdFeB having undergone the HDDR process (“Hydrogenation Disproportionation Desorption Recombination” according to the Anglo-Saxon terminology) which makes it possible to confer a high coercivity on the powder, or even hard ferrites (strontium ferrite for example) or of the SmCo.

The predetermined pressure is for example less than 1000 bars.

The device 10 also comprises polarization modules 40 (FIGS. 1 and 3) regularly distributed, in the form of a crown, called magnetic crown, around the axis of revolution of the cylindrical cavity 20 (FIG. 1). In other words the cylindrical cavity 20 is at the center of the magnetic crown. In the example represented in figure 1, the magnetic ring is made up of 6 polarization modules. However, the invention is not limited to this single configuration.

Each polarization module can advantageously be arranged in correspondence with a different polar series so as to be able to impose the magnetic field on the magnetic composite material capable of being injected into the injection cavities of said polar series.

Each polarization module 40 comprises, along a main axis XX', a magnetic section 42 and a magnetic pole 43. Each polarization module 40 can also comprise a loopback member 41. Each polarization module can in particular reveal in the order and along the main axis XX', the looping member 41, the magnetic section 42 and the magnetic pole 43.

In particular, the magnetic section 42 of each of the polarization modules 40 is intended to impose a magnetic polarization field on the composite material injected in the liquid state into the injection cavities 34a. Maintaining this polarization field until the magnetic composite material freezes by cooling thus makes it possible to form the magnetized sections of the poles of the rotor. The mapping can advantageously be carried out by means of guides. These guides may in particular comprise holes formed from the upper face towards the lower face of the rotor and pins projecting relative to the flat support 60 and intended to impose the orientation of the rotor on the flat support 60.

Magnetic section 42 may include a permanent magnet. However, according to a preferred embodiment of the present invention, the magnetic section 42 may comprise a coil carrier around which is formed a coil which, when passed through by an electric current, generates the magnetic field necessary for the magnetization of the magnetic composite mixture. The winding can in this respect comprise copper wire, while the coil carrier can comprise a magnetic core (for example martensitic steel, FeNi, FeCo or any other soft magnetic alloy). The magnetic section 42 advantageously has, with the loopback member 41, a shape allowing effective loopback of the magnetic flux on the magnetic section itself or with the flux of an immediately adjacent magnetic section (FIG. 6).

In the example shown in Figure 1, the current supply to the windings is adapted so that each polarization module generates a magnetic field opposite to that generated by the modules which are directly adjacent to it. This arrangement thus makes it possible to achieve an alternation of the poles in terms of polarization. Moreover, still in this example, the magnetomotive force of each of the windings can be 10 kA.turns, requiring for each of said windings a total power of approximately 4 kW in direct current. In operation, such power is likely to cause significant overheating. Thus, in order to be able to limit the latter, it is possible to implement a cooling system, for example a system for circulating a heat transfer fluid directly in the coil carrier. The implementation of a cooling system makes it possible in this respect to increase the current likely to pass through each of the windings, and consequently to impose a larger bias field, without having to increase the size of the magnetic crown. .

Consideration of the cooled coil holder/coiling couple makes it possible to form a relatively compact magnetic ring. Furthermore, this magnetic field generation system is controllable so that the magnetic field it generates can be cut at any time, and in particular when the magnetic composite material is completely solidified. The mold can thus be opened under improved safety conditions.

It is thus possible to operate this device under improved safety conditions compared to devices using permanent magnetic magnets.

The magnetic pole 43 of each given polarization module 40 has the shape of a truncated pyramid whose height is parallel to the main direction of the polarization module considered (FIG. 3). In particular, the small base of the truncated pyramid forms a lateral support surface 43a curved so as to match the shape of the lateral section of the rotor. More particularly, all of the lateral holding surfaces 43a, 46a and 46b define a lateral surface 43s of the cylindrical cavity 20 (FIG. 1).

The magnetic pole 43 may include a central section 45 as well as a first side section 46a and a second side section 46b.

In particular, the central section 45 can be inserted between the first lateral section 46a and the second lateral section 46b (FIG. 3). More particularly, within a polarization module 40, the central section 45 made of a magnetic material makes it possible to guide the magnetic field produced at the level of the magnetic section towards the center of a polar series of the rotor, while the first side section 46a and second side section 46b made of a non-magnetic material limit the magnetic leakage between adjacent central sections 45. In particular, the first lateral section 46a and the second lateral section 46b have a much lower magnetic permeability than that of the central section 45, advantageously equal to that of air.

The device 10 according to the present invention can also comprise locking means which make it possible in particular to maintain the lateral holding surfaces 43a, 46a and 46b bearing against the lateral section of the rotor. This support of the lateral support surfaces 43a, 46a and 46b is in particular suitable for compensating for the mechanical stresses likely to be imposed on the rotor during the injection of the composite material at the pressure P. In other words, the means blocking are arranged so that the side surface 43s of the cylindrical cavity 20 opposes the lateral deformation of the rotor during the injection at the pressure P of the magnetic composite mixture.

This aspect is particularly advantageous in particular when the rotor has zones sensitive to deformation under the effect of an internal pressure undergone during the injection of the magnetic composite material. These sensitive areas are particularly induced by the proximity of the injection cavities and the lateral section of the rotor. The only maintenance by the lateral surface, possibly in compression, makes it possible to preserve the mechanical integrity of the rotor during the injection at the pressure P of the magnetic composite mixture.

The blocking means can advantageously comprise jacks which each exert a force concentrically along the main axis of each polarization module 40.

Alternatively, the blocking means may comprise a plurality of inclined rails, for example at an angle of less than 10°, relative to the axis of revolution of the cylindrical cavity 20, and along which the polarization modules are likely to slide. In particular, each polarization module can be associated with one or two rails 50 mechanically linked to the flat support 60 and relative to which said rails project. According to this configuration, each of the polarization modules can slide between two positions called, respectively, high position and low position. The low position being in particular a position for which said modules rest on the flat support. In particular, the inclination of the rails is adapted so that when the polarization modules 40 slide from the high position to the low position, the lateral support surfaces 43a approach each other in order to come into contact with the lateral section of the rotor pre-positioned on the flat support.

The device 10 can also comprise a lower holding member 70 (FIGS. 4a and 4b) and an upper holding member 71 (FIG. 4c) held in abutment (under pressure) by second blocking means against, respectively, the upper face 31 of the rotor and the underside of the rotor. This holding by the upper holding member 71 and by the lower holding member 70 is adapted to compensate for (oppose the) stresses liable to be imposed on the rotor during the injection of the composite material at the pressure p.

The lower and upper holding members can each take the form of a holding plate.

This last aspect is particularly advantageous when the body of the rotor is formed from a stack of sheets. Indeed, the simple implementation of the upper holding member 71 and the lower holding member 70 makes it possible to maintain the sheets joined together, and to limit any infiltration of the magnetic composite material during the step of 'injection.

According to another aspect of the invention, the injection means can be arranged to inject magnetic composite material at the level of the upper face 31 of the rotor 30.

In particular, the injection means can cooperate with the upper holding member 71 for the injection of the magnetic composite material into the injection cavities 34. In this respect and advantageously, the upper holding member 71 may comprise a plurality of distribution channels arranged for the collective injection of the magnetic composite material into each of the magnetic cavities 34, while ensuring axial holding of the rotor by means of surfaces parallel to the upper and lower faces of the rotor. This arrangement makes it possible to inject, at the same time, the same quantity of magnetic composite material into each of the injection cavities so as to balance the stresses undergone by the rotor throughout its volume. In this respect, FIG. 5 represents an imprint E of the distribution channels, made of the fixed magnetic composite mixture.

According to a particular embodiment, the injection cavities of a polar series are symmetrical with respect to a plane formed by the axis of revolution and by the main axis of the polarization module in correspondence with the polar series concerned, and are arranged in several rows one behind the other along said main axis (Figure 2).

In other words, the injection cavities of a polar series are arranged one behind the other in a radial direction. For example, and according to a particular embodiment, the section of an injection cavity along a section plane perpendicular to the axis of revolution and along a radial direction (from the center towards the lateral section) has a concave shape ( for example a full arc shape).

According to such an arrangement, all the injection cavities of a polar series are not equally exposed to the magnetic field imposed by the polarization module. In particular, the cavities closest to the center of the rotor are screened by the cavities located closer to the lateral section of the rotor.

In order to overcome this problem, the device may comprise magnetic field distributor means intended to distribute the magnetic field imposed by each polarization module to the injection cavities of the polar series with which said module.

In particular, these distributor means may comprise inserts 55 intended to produce a magnetic bridge between the polarization module and at least one of the cavities or rows of injection cavities of the polar series in correspondence with said polarization module.

More particularly, these inserts 55 in particular make contact at the level of the magnetic pole and the upper face of the rotor close to an injection cavity, and more particularly between two cavities or rows of injection cavities of a polar series.

These inserts 55 can in particular cooperate with one and the other of the upper holding member 71 and the lower holding member 70. A holding member can comprise orifices 56, opening at the level of a first face, and in which the inserts 55 are positioned. The first face is in particular opposite a second face of the holding member considered intended to be in contact with a face of the rotor 30 (FIGS. 4a and 4b). Orifices 56 advantageously have a shape complementary to inserts 55.

Furthermore, the insert 55 further comprises a protuberance 55a passing through, via a passage 70a, the lower retaining member 70 and emerging at the level of the second face of said member to come into contact with the lower face of the rotor 30. the other end 55b of the inserts comes into contact with the corresponding polarization module so as to form a magnetic bridge with the rotor. In this respect, the inserts advantageously have a higher magnetic permittivity than that of the lower holding member, so that said inserts 55 form a privileged circulation path for the magnetic field imposed by the polarization module. The same arrangement of the inserts 55 is provided in relation to the upper holding member 71 (FIG. 4c).

It is thus possible to better distribute the magnetic field and above all to compensate at least in part for the screening exerted at the level of a given injection cavity by another injection cavity which is interposed between the polarization module and said given injection cavity.

The inserts 55 can thus comprise a soft ferromagnetic alloy (for example martensitic steel, FeCo, FeNi or any other alloy having a high relative permeability – preferably greater than 500 – and a high saturation induction – preferably greater than 1.5T).

The upper retaining member 71 may comprise a perfectly non-magnetic metallic material (for example annealed 316L stainless steel after machining, Inconel, copper and/or aluminum alloys, brass, etc.).

Figure 6 is a schematic representation of the device 10 according to the present invention.

In particular, this figure represents the distribution of the magnetic field lines (in the form of arrows) created by the windings B.

Figure 7 is a graphic representation of a simulation and a measurement of the magnetic field (along the horizontal axis in "mT") as a function of the angular position (horizontal axis in degrees) at the level of the lateral section of the rotor manufactured with the device according to the present invention. The two curves representative of the magnetic field overlap perfectly, indicating in particular the good understanding and the performance of the pole-forming device according to the present invention.

Claims (11)

Device (10) for forming poles of a rotor (30), each pole comprising one or more magnetized sections formed in a series of injection cavities (34a), called the pole series, of the rotor (30), by injection of a composite material in said cavities, the device (10) comprises:
- a rotor (30), arranged in a cylindrical cavity (20), said rotor (30) being delimited by an upper face (31) and a lower face which are flat and parallel to each other, and connected by a lateral section (33) of cylindrical in shape, the polar series have a regular angular distribution around an axis of revolution of said rotor (30), and the injection cavities (34a) open out at the level of the lower face and the upper face (31);
- a means of injecting magnetic composite material, in the liquid state, into the injection cavities (34a) at a pressure P lower than a predetermined pressure;
- polarization modules regularly distributed around the axis of revolution of the cylindrical cavity (20), each polarization module (40) comprising, in order and along a main axis, a feedback member (41), a magnetic section (42) intended to impose a magnetic polarization field on the composite material capable of being injected into the injection cavities (34a), and a magnetic pole (43), the magnetic poles comprising a surface, called surface of lateral support (43a), the set of lateral support surfaces defining a lateral surface (43s) of the cylindrical cavity (20);
- locking means arranged so as to maintain the lateral support surfaces bearing against the lateral section (33) of the rotor (30), so that the lateral support surfaces compensate for the stresses imposed on the rotor (30) during the injection of the composite material at the pressure P. Device (10) according to Claim 1, in which each polarization module (40) is arranged in correspondence with a different polar series so as to be able to impose the magnetic field on the magnetic composite material capable of being injected into the cavities of injection (34a) of said polar series. Device (10) according to Claim 1 or 2, in which the said device (10) comprises an upper holding member (71) and a lower holding member (70) held in abutment by second locking means against, respectively, the upper face (31) and the lower face, and so as to compensate for the stresses liable to be imposed on the rotor (30) during the injection of the composite material at the pressure P. Device (10) according to Claim 3, in which the injection means is arranged to inject magnetic composite material at the level of the upper face (31) of the rotor (30). Device (10) according to Claim 3 or 4, in which the injection means cooperates with the upper holding member (71) for the injection of the magnetic composite material into the injection cavities (34a). Device (10) according to Claim 5, in which the upper holding member (71) comprises a plurality of distribution channels arranged for the collective injection of the magnetic composite material into each of the injection cavities (34a). Device (10) according to one of Claims 3 to 6, in which the injection cavities (34a) of a polar series are symmetrical with respect to a plane formed by the axis of revolution and by the main axis of the polarization module (40) in correspondence with the polar series concerned, and are arranged one behind the other along said main axis, the device (10) comprises magnetic field distributor means intended to distribute the magnetic field imposed by each module polarization (40) to the injection cavities (34a) of the polar series with which said module (40) is in correspondence. Device (10) according to claim 7, in which the distributing means comprise inserts 55, each insert forming a magnetic bridge between a polarization module (40) and injection cavities (34a) of the polar series with which said module (40) is matched. Device (10) according to claim 8, in which the magnetic bridge is made between the polarization module (40) and injection cavities of the series of polars likely to be screened by other injection cavities (34a ) of this same polar series. Device (10) according to Claim 9, in which the inserts 55 are inserted into orifices 56 of the upper holding member (71) and of the lower holding member (70), and advantageously comprise a ferromagnetic material. Device (10) according to one of Claims 1 to 10, in which the magnetic section (42) comprises a coil carrier around which is formed a coil which, when passed through by an electric current, generates the magnetic field necessary for the magnetization of the magnetic composite mixture capable of being injected into the injection cavities (34a).